Add support for controlling the "compat" app icon shape

[mattleibow]

Description

In Android 8.0 (API 26), the OS added support for adaptive icons. Resizetizer handles this just fine, however when it generates the backwards compat icon, it is just a square - or more specifically it is just drawing the background as is.

The Android 8.0 OS has some options:

But for older version of the OS, the developer is responsible for generating the "shape". For example, in Android Studio:

As you can see, there is both a round icon and a legacy icon. We already have the round adaptive icon, but still need to add the legacy versions of both the actual round image and then the shaped image (square - current, squircle, rounded square, circle)

There is also an app that can be used to test many variations: https://github.com/nickbutcher/AdaptiveIconPlayground

In summary, we have:

• [x] Adaptive shaped
• [x] Adaptive round
• [x] Legacy none

We are missing:

• [ ] Legacy round
• [ ] Legacy shaped (square, squircle, circle, rounded square)
• [ ] Legacy alternate shaped (vertical, horizontal)

Public API Changes

Maybe all we need is an optional parameter on <MauiIcon Shape="xxx" />

This would then be a choice of a few things:

• None (current and default)
• Square
• Circle
• Rounded Square
• Squircle
• Vertical
• Horizontal

Intended Use-Case

More things to support typical scenarios.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.